[1969GPSJ]

Franked, I could be wrong, but IMO, and strongly suggested by current production engines and typical, recent hot rod builds of aluminum head engines, your machinist is in left field, crap gas or not. An engine built with aluminum head is significantly more tolerant of poor octane fuel than an engine with iron heads, even without regard to the dynamic compression influence via camshaft timing. The much higher heat loss rate associated with the aluminum heads significantly reduces the chances for detonation. Most non-turbo V8 builds now with aluminum heads are comfortably running compression ratios at (or above) 10.5:1 on 89-91 octane fuel - as long as the fuel/air mixture is not really messed up. I would seek out the direct advice from either the folks at Butler, Kauffman or Don at DCI. motorsports. For a small example, my wife's mini-van has 11.3:1 compression and is comfortable with 89 octane fuel, and makes over 280 hp (stock) with only 3.6 liters (non mini-van versions are rated at 310 HP). Granted it was designed with variable valve timing, 4 valves per cylinder, electronically controlled fuel injection and ignition, and a modern head design. The 2 liter Turbo Direct Injected 4 cylinder in my daughters car makes 200 (stock) hp with 10.5:1 compression (but requires 91 octane fuel). The aluminum Kauffman D port heads are said to have an excellent chamber configuration, that is highly detonation resistant, and that combined with being aluminum makes running 105:1 compression roughly the iron-head equivalent of 8.5:1 (I'm sure that the folks at Kauffman can give you a better number than that).